Lucy spent so much time in trees

Lucy, the first complete skeleton of the erliest hominid ever found, is suggested to have been a very good climber. Her fossil, which is 3,18 million-years-old, is what give the researchers the clue about this fact.

“Most people have agreed for a while that she did some tree climbing, or had done tree climbing in the recent past, but there were a lot of questions about whether it was a major part of her lifestyle,” said Christopher Ruff, a professor of functional anatomy and evolution at Johns Hopkins University School of Medicine and the lead author on the study. “We’re saying she probably used trees on a daily basis.”

The authors turned to a micro-CT scan of Lucy’s skeleton to come to this conclusion. Lucy’s fossilized bones had been scanned not long after their discovery in the early 1970s, but the instruments back then were not powerful enough to show the internal structure of her bones.

Being able to peer into the interior of Lucy’s bones has shed a whole new light on how Lucy lived her life, Ruff said.

Ruff and his team concentrated on cross-sectional scans of Lucy’s one remaining thigh bone and her two remaining upper arm bones. In particular, they were looking for how tissue was distributed along the bone shaft as an indication of strength.

Next, the group compared the relative strength of Lucy’s bones to those from a database of more than 1,000 pre-20th century humans and 100 chimpanzees.

Previous work on chimpanzees and gorillas revealed that measurements like these matched up with locomotion behavior.

For example, animals that climbed trees had relatively stronger upper limbs compared with those that did not climb trees.

The authors found that Lucy’s upper limb strength was intermediate between humans and chimps, but a bit closer to the chimp side. This suggests that she used her upper limbs significantly more than we do, although not as much as chimpanzees, which frequently climb trees.

He added that it is hard to imagine what other factors besides tree climbing would have created the bone tissue distribution he observed in Lucy’s upper arm bones.

“There is really no other explanation for that kind of overloading,” Ruff said.

Divulgation article: http://www.nytimes.com/2016/11/30/science/lucy-bones-trees.html?rref=collection%2Ftimestopic%2FArchaeology%20and%20Anthropology&action=click&contentCollection=science&region=stream&module=stream_unit&version=latest&contentPlacement=4&pgtype=collection&_r=0

Original article: http://journals.plos.org/plosone/article?id=info%3Adoi/10.1371/journal.pone.0166095

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